Math Problem Statement

The rectangles in the graph below illustrate a left endpoint Riemann sum for f(x) = x^2/11 on the interval [2, 6]. The value of this left endpoint Riemann sum is ___, and this Riemann sum is ___ the area of the region enclosed by y = f(x), the x-axis, and the vertical lines x = 2 and x = 6.

Solution

To solve this, let's compute the left endpoint Riemann sum for the function f(x)=x211f(x) = \frac{x^2}{11} on the interval [2,6][2, 6], divided into equal subintervals.


Step 1: Divide the interval

  • The interval [2,6][2, 6] has 4 subintervals.
  • Subinterval width (Δx\Delta x) is: Δx=624=1\Delta x = \frac{6 - 2}{4} = 1

Step 2: Identify left endpoints

The left endpoints of the subintervals are: x=2,3,4,5x = 2, 3, 4, 5


Step 3: Evaluate f(x)f(x) at each left endpoint

Substitute each left endpoint into f(x)=x211f(x) = \frac{x^2}{11}:

  • f(2)=2211=411f(2) = \frac{2^2}{11} = \frac{4}{11}
  • f(3)=3211=911f(3) = \frac{3^2}{11} = \frac{9}{11}
  • f(4)=4211=1611f(4) = \frac{4^2}{11} = \frac{16}{11}
  • f(5)=5211=2511f(5) = \frac{5^2}{11} = \frac{25}{11}

Step 4: Compute the Riemann sum

The left endpoint Riemann sum is: Sum=Δx[f(2)+f(3)+f(4)+f(5)]\text{Sum} = \Delta x \cdot \left[ f(2) + f(3) + f(4) + f(5) \right] Substitute values: Sum=1(411+911+1611+2511)\text{Sum} = 1 \cdot \left( \frac{4}{11} + \frac{9}{11} + \frac{16}{11} + \frac{25}{11} \right) Combine terms: Sum=4+9+16+2511=5411\text{Sum} = \frac{4 + 9 + 16 + 25}{11} = \frac{54}{11}

Thus, the value of the left endpoint Riemann sum is: 5411or approximately 4.91\boxed{\frac{54}{11} \, \text{or approximately } 4.91}


Let me know if you'd like further clarification or details!
Here are related questions you might explore:

  1. How do you compute right endpoint Riemann sums for a function?
  2. What happens to the Riemann sum as the number of subintervals increases?
  3. Can this Riemann sum approximate the exact integral of f(x)f(x)?
  4. How does the choice of endpoints affect the sum?
  5. How do Riemann sums relate to definite integrals in calculus?

Tip: For better approximations, try using midpoint Riemann sums or evaluate the definite integral analytically.

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Math Problem Analysis

Mathematical Concepts

Riemann Sum
Definite Integral Approximation
Piecewise Function Analysis

Formulas

Left Endpoint Riemann Sum: Sum = Δx × Σ[f(x_left)]

Theorems

Definition of a Definite Integral

Suitable Grade Level

Grades 11-12